Plate divergence in Iceland

Jacques Angelier

Keywords: inversion, stress, paleostress, trajectory, divergence, extension, volcanism, magmatism, displacement, kinematics, dynamics, tensor, slip, fault, rifting, ocean, ridge, rift, tectonics, seismotectonics, focal mechanism, mapping, cross-section, brittle structures, field work, geology, data base, multiphase, right dihedra, North Atlantic, plate tectonics, lithosphere, glacier, glaciation, historical seismicity, reconstruction, mechanical coupling

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Distribution of seismotectonic stress in Iceland (green arrows indicate extension) as a function of rift segment distribution. Yellow arrows indicate plate motion with respect to Mid-Atlantic Ridge. Source: ANGELIER J., SLUNGA R. F., BERGERAT F., STEFANSSON R. and HOMBERG C. (2004) – Perturbation of stress and oceanic rift extension across transform faults shown by earthquake focal mechanisms in Iceland. Earth Planet. Sci. Letters, 219, p. 271-284, 7 fig., 2 tabl.

 

The Tjörnes Fracture Zone, an active rigth-lateral transform zone. Eight stress regimes occur with different trends as a function of variable mechanical coupling across transform fault (four normal regimes and four strike-slip ones). Source: ANGELIER J., BERGERAT F. and HOMBERG C. (2000). - Variable coupling across weak oceanic transform fault: Flateyjarskagi, Iceland. Terra Nova, 12, p. 97-101, 4 fig., 1 tabl.  

 

Surface features along a post-glacial fault in Iceland. Source: ANGELIER J., BERGERAT F., BELLOU M. and HOMBERG C. (2004) - Co-seismic strike-slip fault displacement determined from push-up structures : the Selsund Fault case, South Iceland. Journ. Struct. Geol., 26, p. 709-724, 14 fig., 4 tabl.

 

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Distribution of earthquakes along N-S trending, right-lateral faults in the E-W trendingSouth Iceland Seismic Zone. Seismological data from the SIL network of the Icelandic Meteorological Institute. Epicentres mapped using the 2007 Tector softwares (CARTAX, Tector 2000 series).

  

 Depth distribution of the 33,878 earthquakes mapped above, as illustrated with program ROSACE (version 2006, Tector 2000 series). Histogram with depth classes of 2 km. Source: ANGELIER J., BERGERAT F., STEFANSSON R. and BELLOU M. (2007). - Seismotectonics of a newly formed transform zone near a hotspot: earthquake mechanisms and regional stress in the South Iceland Seismic Zone, Tectonophysics, in press.

 

Model  of development of an incipient shear zone (such as the South Iceland Seismic Zone). Note the early development of N-S dextral faults across the E-W sinistral shear zone, then the growth of Riedel additive faults and the late individualisation of the major fault. Whereas the present-day South Iceland Seismic Zone is between stages (a) and (b), the right-lateral Husavik Fault of the Tjörnes Fracture Zone has reached stage (c). Source: ANGELIER J., BERGERAT F., BELLOU M. and HOMBERG C. (2004) - Co-seismic strike-slip fault displacement determined from push-up structures : the Selsund Fault case, South Iceland. Journ. Struct. Geol., 26, p. 709-724, 14 fig., 4 tabl.

 

Mechanical consistency of active faults in the South Iceland Seismic Zone. Black arrows indicate strike-slip movements, yellow arrows illustrate the left-lateral movement along the E-W transform fault, red arrows show the seismotectonic stress directions in and around the transform zone. Source: ANGELIER J. and BERGERAT F. (2002) - Behaviour of a rupture of the 21 June 2000 earthquake in South Iceland as revealed in an asphalted car park. Journ. Struct. Geol., 24, p. 1925-1936, 10 fig.

 

Example of multiscale strike-slip faulting pattern in the South Iceland Seismic Zone, June 2000 earthquakes. (a) Anticlockwise rotation of small road induced by left-lateral shear, decametric scale. (b) Asphalted car park offset by E-W trending left-lateral strike-slip fault., hectometric scale. (c) Anticlockwise rotation of blocks bounded by N-S trending right-lateral strike-slip faults, decakilometric scale. (d) Left-lateral transform movement along the E-W trending South Iceland Seismic Zone between the Rekjanes Ridge and the East Volcanic Zone of Iceland. Source:  ANGELIER J. and BERGERAT F. (2002) - Behaviour of a rupture of the 21 June 2000 earthquake in South Iceland as revealed in an asphalted car park. Journ. Struct. Geol., 24, p. 1925-1936, 10 fig.

 

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Mots-clés: inversion, contrainte, paléocontrainte, trajectoire, divergence, extension, volcanisme, magmatisme, déplacement, cinématique, dynamique, tenseur, glissement, faille, rifting, océan, ride, rift, tectonique, sismotectonique, mécanisme au foyer, cartographie, coupe, structures cassantes, étude de terrain, géologie, base de données, polyphasage, dièdres droits, Atlantique Nord, tectonique de plaques, lithosphère, glacier, glaciation, sismicité historique, reconstruction, couplage mécanique